As for the means for connecting electronic parts to each other, anisotropic conductive films (ACFs) have been conventionally used.
The anisotropic conductive film is produced by applying a resin mixture containing conductive particles onto a release film, and drying the resin mixture. A method for connecting between electronic components is a method where the anisotropic conductive film formed on the release film is placed on one of circuits to be connected (or both circuits to be connected), the predetermined temperature and pressure are applied from the side of the release film to temporarily bond, the release film is peeled, the resultant is positioned on the other circuit, and the predetermined temperature and pressure are applied for the predetermined period to bond (or temporary-bonding may be performed at the predetermined temperature and pressure for the predetermined period after the positioning, followed by performing bonding) to thereby perform electric connection between the circuits.
In order to improve workability of an assembling step for electronic components and to enable highly reliable electric connection in temporary bonding before peeling a release film or temporary bonding before final bonding, the conductive particle-containing layer needs to have sufficient adhesion. This is because the conductive particle-containing layer is peeled off from a circuit board to be connected when the release film is peeled, if adhesion of the conductive particle-containing layer in the anisotropic conductive film is poor. Moreover, the conductive particle-containing layer and the release film may be peeled off from each other, for example, when the release film has high releasability and the anisotropic conductive film is pulled out from a roll for use. If the releasability of the release film is poor, the conductive particle-containing layer is peeled off together with the release film, when the release film is peeled off after temporary-bonding. Therefore, it is important that the conductive particle-containing layer and the release film have appropriate releasability and adhesion.
Accordingly, there is a need for an anisotropic conductive film having excellent temporary-fixing properties satisfying the aforementioned demands at the time of temporary-bonding. For example, an anisotropic conductive film whose temporary-bonding properties have been improved by blending a liquid epoxy resin into a thermoset resin is known (see PTL 1).
However, the proposed anisotropic conductive film is not satisfactory in terms of practical use and workability, and needs further improvements.
Moreover, there has recently been a demand for connecting electronic components to each other at a low temperature for a short period. Therefore, non-reaction-type anisotropic conductive films that enable to connect electronic components at a low temperature for a short period have been studied.
It has been however found that heat resistance of a non-reaction-type anisotropic conductive film is significantly impaired, if a liquid material, such as a material used in the aforementioned thermoset resin anisotropic conductive film, is blended in the non-reaction-type anisotropic conductive film to improve temporary-fixing properties. The non-reaction-type anisotropic conductive film has a problem that a problem associated with temporary-fixing properties becomes significant.
Accordingly, there is a need for a non-reaction-type anisotropic conductive film having excellent temporary-fixing properties.
Moreover, anisotropic conductive films have been conventionally used for connection of fine wirings unsuitable for solider connection. Since low temperature connection is realized, anisotropic conductive films have been used for connection of relatively rough wirings.
An anisotropic conductive film originally designed for fine wirings is bonded with a small area, and achieves conduction, as a conductive particle-containing layer is flown outside a terminal region by squashing a binder forming the conductive particle-containing layer to make a thickness of the conductive particle-containing layer thinner than diameters of conductive particles, and as a result, the conductive particles are crushed. In the case where a terminal region of a relative large area is attempted to be connected, however, a curing reaction is caused at around a center part of the conductive particle-containing layer of the large area to increase viscosity before flowing into outside the terminal region, and thus the conductive particle-containing layer is not flown outside the terminal region and cannot be made thin. Therefore, the conductive particles are not crushed sufficiently, and excellent conduction cannot be obtained.
On the other hand, non-reaction-type anisotropic conductive films, which do not carry out a curing reaction, do not increase viscosity along with a curing reaction. Accordingly, the non-reaction-type anisotropic conductive films do not have the aforementioned problem, and can achieve excellent conduction.
In case of the non-reaction-type anisotropic conductive films, however, there are problems that tackiness is low and the aforementioned temporary-fixing properties are poor because the non-reaction-type anisotropic conductive film contains a crystalline material having a melting point.